Instantiate prefab once help C#

Hi, I'm trying to spawn a health object when the players health is 15 or less but my instantiate creates a loop if I don't pick up the health object instantly. Could anyone help me please?

Code lines: 14, 15, 30, 31, 32, 33, 34, 35, 36, 37

 using UnityEngine;
 using System.Collections;
 
 public class Player_Health : MonoBehaviour {
 
     public static float curHealth = 100f;
     public static float maxHealth = 100f;
     public static float decHealth = 5f;
     public static float regHealth = 1f;
 
     public static bool levelFail = false;
     public GUISkin skin;
 
     public GameObject spawnHealth;
     public bool completedHealth;
 
     void Start(){
         curHealth = 1;
         }
 
     void Update(){
         if (curHealth < maxHealth) 
         {
             curHealth += regHealth * Time.deltaTime;
         }
         if (curHealth <= 0) 
         {
             levelFail = true;
         }
         if (curHealth <= 15) 
         {
             completedHealth = true;
             if(completedHealth = true)
             {
                 Instantiate(spawnHealth);
                 completedHealth = false;
             }
 
         }
     }
 
     void OnTriggerStay2D(Collider2D other){
         if (other.gameObject.tag == "Darkness") 
         {
             curHealth -= decHealth * Time.deltaTime;
         }
     }
     void OnTriggerEnter2D(Collider2D other){
         if (other.gameObject.tag == "Health") 
         {
             Player_Health.curHealth = maxHealth;
             Destroy(other.gameObject);
         }
     }
 
 
     void OnGUI(){
         GUI.skin = skin;
         string HealthText = "Your Health: " + curHealth + " / " + maxHealth;
         GUI.Box (new Rect(Screen.width /2 - 350, 20, 200, 24), HealthText);
 
         if (levelFail == true)
         {
             Time.timeScale = 0;
             Rect winScreenRect = new Rect(Screen.width/2 - (Screen.width *.5f/2), Screen.height/2 - (Screen.height *.5f/2), Screen.width *.5f, Screen.height *.5f);
             GUI.Box(winScreenRect, "Level Failed!");
             
             if (GUI.Button(new Rect(winScreenRect.x + winScreenRect.width - 170, winScreenRect.y + winScreenRect.height - 60, 150, 40), "Retry"))
             {
                 Destroy(gameObject);
                 Application.LoadLevel(Application.loadedLevel);
                 Game_Manager.lightsActive = 0;
                 curHealth = 100f;
                 levelFail = false;
                 Time.timeScale = 1;
                 EndLvl.curHealthGuard = EndLvl.maxHealthGuard;
             }
             if (GUI.Button(new Rect(winScreenRect.x + 20, winScreenRect.y + winScreenRect.height - 60, 100, 40), "Quit"))
             {
                 Application.LoadLevel(0);
             }
             
         }
     }
 
 }